Elevator systems are widely known and used. Typical arrangements include an elevator cab that moves between landings in a building, for example, to transport passengers or cargo between different building levels. A motorized elevator machine moves a rope or belt assembly, which typically supports the weight of the cab, and moves the cab through a hoistway.
The elevator machine includes a machine shaft that is selectively rotationally driven by a motor. The machine shaft typically supports a sheave that rotates with the machine shaft. The ropes or belts are tracked through the sheave such that the elevator machine rotates the sheave in one direction to lower the cab and rotates the sheave in the opposite direction to raise the cab. The elevator machine also includes a brake that engages a disk or a flange that rotates with the machine shaft to hold the machine shaft and sheave stationary when the cab is at a selected landing.
Typical elevator systems include a controller that collects cab weight information and controls the elevator machine based upon the weight information. The controller typically receives the weight information from load-measuring devices installed in the floor of the car. Disadvantageously, floor-installed load-measuring devices often do not provide accurate enough weight information. When the weight in the cab is small, for example, floor-installed load-measuring devices may not accurately distinguish between the background weight of the cab and the small load. Also a load not centered in the cab will not give accurate weight information. Additional load-measuring devices may be used to increase the accuracy, however, the expense and maintenance of the elevator system increases with each additional device. Changes to the elevator such as counterweight loads or modifications to the car are not accounted for by the floor sensors.
Other elevator systems utilize the elevator brake to indicate the weight on the car. Typically, these systems utilize a load cell leveraged between the brake and the floor of the elevator machine room. The torque resulting from application of the brake results in a load on the load cell. Disadvantageously, these systems require a large amount of space in the elevator machine room, are inaccurate by the brake or machine weight added to the load cell amount, and may be expensive. Elevator brakes and load cells in this type of configuration may also cease to operate properly under high levels of torque, which may lead to undesirable conditions in the elevator system. One proposed solution includes making the load cells larger and more robust, however, this may lead to a loss of sensitivity in indicating the weight in the cab.
There is a need for a strong, compact, and sensitive system for providing elevator cab weight information. This invention addresses those needs and provides enhanced capabilities while avoiding the shortcomings and drawbacks of the prior art.